A header for a crop harvesting machine generally comprises a main longitudinal support member in the form of an elongate tube which extends across substantially the full width of the header frame and defines a main structural member for the header frame. The tube carries a plurality of forwardly and downwardly extending support beams which include a first portion extending downwardly and a second portion attached to a lower end of the first portion and extending forwardly therefrom toward a forward end of the support beams. The cuter bar is attached to the forward end of the support beams and is thus held thereby in a position generally parallel to the main support tube.
Many headers are of a type in which the cutter bar is intended to be in a fixed rigid position relative to the main support tube so that the cutter bar is not intended to flex or float relative to the main structural tube in response to changes in ground contour.
This rigid type of header has the advantage that it allows more accurate control of the position of the fingers or bats of the reel relative to the cutter bar so as to more accurately control the crop as it is swept onto the cutter bar and the table rearwardly of the cutter bar.
In this rigid header type, therefore, the support beams extending forwardly from the main structural tube are substantially rigid and hold the cutter bar in fixed position.
Alternative types of header mount the cutter bar for floating or flexing movement relative to the main structural support tube. This type of header is used to provide an improved action in following the contour of the ground and is advantageous in some circumstances. This type of header however has the disadvantage that the flexing or floating of the cutter bar relative to the main support tube causes movement of the cutter bar relative to the bats or fingers of the reel so that it is no longer possible to maintain a close tolerance between the bats or fingers and the cutter bar.
Various manufacturers provide a flexing cutter bar structure for example the Soybean Header manufactured by Case IH under the serial No 820 or 1020.
Other types of header provide a cutter bar which is relatively rigid but can float upwardly and downwardly relative to the main structural support tube of the header. This type of header again is used to allow close floating action of the cutter bar on the ground surface and one example is shown in the "Dial-a-matic Header Height Control" available for various Deere and Company combine harvesters. This floating action of a cutter bar however occurs relative to the main structural tube and therefore relative to the reel so that the cutter bar to reel cooperation cannot be optimized.
The present invention is not concerned with the floating or flexing type cutter bar described above but is instead directed to an arrangement in which the main structural tube and support beams are intended to hold the cutter bar substantially rigid and fixed relative to the main structural support tube so as to allow an optimization of the cooperation between the reel and the cutter bar.
However, as the width of headers has increased in recent years, the amount of flexing of the structure of the header which occurs has necessarily increased.
In general the header frame structure includes a central pair of inner support beams each spaced outwardly from a midpoint of the main structural tube and at least one outer pair of support beams which are arranged at or adjacent the outer ends of the main structural tube. In some headers additional support beams can be positioned between in the inner and outer support beams to provide additional structural support.
The header frame is generally attached to the support vehicle, either a tractor or a combine harvester, by attachment of the inner pair of support beams to suitable support elements on the vehicle. The outer support beams and the outer parts of the main support tube are therefore cantilevered outwardly from this support structure and thus have a tendency to flex downwardly due to the weight of the elements themselves and the further structure of the header carried on those elements. In particular the reel of the header is generally carried on reel arms which are supported on the main support tube at or adjacent the ends of the main support tube so as to apply a significant weight to the main support tube at the ends thus causing the ends to flex downwardly under that weight.
In addition headers can be used with different types of reel depending upon the requirements of the farmer.
In order to accommodate this downward flexing of the outer ends of the structure, in initial manufacture, the support beams are welded to the main support tube so that, in an unstressed condition, the cutter bar is upwardly concave, that is the centre part is lower than the two ends of the cutter bar.
When the header is fully assembled onto the carrier vehicle, the weight of the frame tends to flex the frame so as to tend to reduce the concave shape. If the calculations are done correctly and the weight of the reel is properly known, it is possible to arrange the header so that when assembled the cutter bar is straight.
However various components of the header can vary so that the accurate weight of the reel and other elements is not properly known. It is not possible, therefore, in all cases to properly calculate the required concave shape and in some cases, therefore, the cutter bar may flex beyond a straight condition into an upwardly convex shape in which the ends are lower than the centre.
While these flexing movements are relatively small, generally less than one inch across the full width of a header, they can interfere with the optimization of the relationship between the reel and the cutter bar. This occurs particularly if the cutter bar is upwardly convex when installed since any upward flexing movement of the centre part of the cutter bar is added to corresponding downward movement of the outer ends of the cutter bar and the reel so that the total relative movement between the reel and the cutter bar is increased. The preferred longitudinal shape of the cutter bar in the installed condition is therefore either straight or slightly upwardly concave.